﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PefStudio.SegyViewer
{
    class Utils
    {
        /// <summary>
        /// 
        /// </summary>
        private static readonly byte[] EToA =
            { 0, 1, 2, 3, 156, 9, 134, 127, 151, 141,
            142, 11, 12, 13, 14, 15, 16, 17, 18, 19, 157,
            133, 8, 135, 24, 25, 146, 143, 28, 29, 30, 31,
            128, 129, 130, 131, 132, 10, 23, 27, 136, 137, 138,
            139, 140, 5, 6, 7, 144, 145, 22, 147, 148, 149,
            150, 4, 152, 153, 154, 155, 20, 21, 158, 26, 32,
            160, 161, 162, 163, 164, 165, 166, 167, 168, 91, 46,
            60, 40, 43, 33, 38, 169, 170, 171, 172, 173, 174,
            175, 176, 177, 93, 36, 42, 41, 59, 94, 45, 47,
            178, 179, 180, 181, 182, 183, 184, 185, 124, 44, 37,
            95, 62, 63, 186, 187, 188, 189, 190, 191, 192, 193,
            194, 96, 58, 35, 64, 39, 61, 34, 195, 97, 98,
            99, 100, 101, 102, 103, 104, 105, 196, 197, 198, 199,
            200, 201, 202, 106, 107, 108, 109, 110, 111, 112, 113,
            114, 203, 204, 205, 206, 207, 208, 209, 126, 115, 116,
            117, 118, 119, 120, 121, 122, 210, 211, 212, 213, 214,
            215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225,
            226, 227, 228, 229, 230, 231, 123, 65, 66, 67, 68,
            69, 70, 71, 72, 73, 232, 233, 234, 235, 236, 237,
            125, 74, 75, 76, 77, 78, 79, 80, 81, 82, 238,
            239, 240, 241, 242, 243, 92, 159, 83, 84, 85, 86,
            87, 88, 89, 90, 244, 245, 246, 247, 248, 249, 48,
            49, 50, 51, 52, 53, 54, 55, 56, 57, 250, 251,
            252, 253, 254, 255 };

        public static int EBCDICToASCII(int ebcdic)
        {
            return EToA[ebcdic & 0xff] & 0xff;
        }

        //
        // 字节流的EBCDIC->ASCII转换函数
        //
        public static byte[] EBCDICToASCII(byte[] ebcdic)
        {
            var tobytes = new byte[ebcdic.Length];
            for (int i = 0; i < ebcdic.Length; i++) tobytes[i] = (byte)EBCDICToASCII(ebcdic[i]);
            return tobytes;
        }

        public static int ReadBigEndianInt32(byte[] bytes, int start)
        {
            var byte4 = new byte[4];
            byte4[0] = bytes[start + 3];
            byte4[1] = bytes[start + 2];
            byte4[2] = bytes[start + 1];
            byte4[3] = bytes[start];

            return BitConverter.ToInt32(byte4, 0);
        }

        public static int ReadBigEndianInt16(byte[] bytes, int start)
        {
            var byte2 = new byte[2];
            byte2[0] = bytes[start + 1];
            byte2[1] = bytes[start];

            return BitConverter.ToInt16(byte2, 0);
        }

        public static byte[] Swapbytes(byte[] bytes)
        {
            if (bytes.Length == 4)
            {
                byte tempb = bytes[0];
                bytes[0] = bytes[3];
                bytes[3] = tempb;
                tempb = bytes[1];
                bytes[1] = bytes[2];
                bytes[2] = tempb;
            }
            else if (bytes.Length == 2)
            {
                byte tempb = bytes[0];
                bytes[0] = bytes[1];
                bytes[1] = tempb;
            }

            return bytes;
        }

        public static Single ReadIEEESingle(byte[] bytes)
        {
            return BitConverter.ToSingle(Swapbytes(bytes), 0);
        }
    }
}
